Variable geometry diffuser ring

ABSTRACT

A compressor includes an impeller, a diffuser passage having a diffuser vane therein, and a variable geometry diffuser ring positioned between the impeller and the diffuser vane with respect to a flow of a refrigerant through the compressor. The compressor also includes an actuator configured to move the variable geometry diffuser ring in a direction transverse to the flow of the refrigerant, and between a plurality of ring positions including a fully retracted ring position in which the variable geometry diffuser ring does not block the flow of the refrigerant, and at least one protruded ring position in which the variable geometry diffuser ring adjusts an angle of the flow of the refrigerant upstream of the diffuser vane.

BACKGROUND

This application relates generally to vapor compression systems incorporated in air conditioning and refrigeration applications, and, more particularly, to flow control of refrigerant in a compressor.

Vapor compression systems are utilized in residential, commercial, and industrial environments to control environmental properties, such as temperature and humidity, for occupants of the respective environments. The vapor compression system circulates a working fluid, typically referred to as a refrigerant, which changes phases between vapor, liquid, and combinations thereof in response to being subjected to different temperatures and pressures associated with operation of the vapor compression system. For example, the vapor compression system utilizes a compressor to circulate the refrigerant to a heat exchanger which may transfer heat between the refrigerant and another fluid flowing through the heat exchanger. Traditional compressors may operate most efficiently when operating at full capacity, but may be configured to operate at different capacities based on various operating and environmental conditions. In other words, at certain operating capacities, an efficiency of the traditional compressor may be reduced.

SUMMARY

In one embodiment, a compressor includes an impeller, a diffuser passage having a diffuser vane therein, and a variable geometry diffuser ring positioned between the impeller and the diffuser vane with respect to a flow of a refrigerant through the compressor. The compressor also includes an actuator configured to move the variable geometry diffuser ring in a direction transverse to the flow of the refrigerant, and between a plurality of ring positions including a fully retracted ring position in which the variable geometry diffuser ring does not block the flow of the refrigerant, and at least one protruded ring position in which the variable geometry diffuser ring adjusts an angle of the flow of the refrigerant upstream of the diffuser vane.

In another embodiment, a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system includes a compressor having a diffuser vane, and having a variable geometry diffuser ring positioned upstream of the diffuser vane with respect to a flow of a refrigerant therethrough. The system also includes a controller configured to control a position of the variable geometry diffuser ring based at least in part on an operating capacity of the compressor and at least in part on an incidence angle of a leading edge of the diffuser vane.

In another embodiment, a method of operating a compressor includes detecting a temperature of a refrigerant, and determining, via a controller, an operating capacity of the compressor based at least in part on the temperature of the refrigerant. The method also includes controlling a position of a variable geometry diffuser ring based at least in part on the operating capacity of the compressor and at least in part on an incidence angle of a leading edge of a diffuser vane of the compressor.

DRAWINGS

FIG. 1 is a perspective view of an embodiment of a building that may utilize a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system in a commercial setting, in accordance with an aspect of the present disclosure;

FIG. 2 is a perspective view of a vapor compression system, in accordance with an aspect of the present disclosure;

FIG. 3 is a schematic of an embodiment of the vapor compression system of FIG. 2, in accordance with an aspect of the present disclosure;

FIG. 4 is a schematic of an embodiment of the vapor compression system of FIG. 2, in accordance with an aspect of the present disclosure;

FIG. 5 is a cross-section of an embodiment of a portion of a compressor that may be included in the systems of FIGS. 1-4, in accordance with an aspect of the present disclosure;

FIG. 6 is a cross-section of a portion of the compressor of FIG. 5, taken along line 6-6 in FIG. 5, in accordance with an aspect of the present disclosure;

FIG. 7 is a cross-section of an embodiment of a portion of a variable geometry diffuser ring for use in the compressor of FIG. 5, in accordance with an aspect of the present disclosure;

FIG. 8 is a cross-section of an embodiment of a portion of a variable geometry diffuser ring for use in the compressor of FIG. 5, in accordance with an aspect of the present disclosure;

FIG. 9 is a cross-section of an embodiment of a portion of a variable geometry diffuser ring for use in the compressor of FIG. 5, in accordance with an aspect of the present disclosure;

FIG. 10 is a cross-section of an embodiment of a variable geometry diffuser ring positioned in a portion of the compressor of FIG. 5, in accordance with an aspect of the present disclosure; and

FIG. 11 is a block diagram illustrating an embodiment of a method of operating a compressor, in accordance with an aspect of the present disclosure.

DETAILED DESCRIPTION

One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

Embodiments of the present disclosure are directed toward a heating, ventilating, air conditioning, and refrigeration (HVAC&R) system that uses a compressor (e.g., centrifugal compressor) to circulate refrigerant through a refrigerant loop. The compressor may be configured to convert a kinetic energy of the flow of refrigerant into pressure. Unfortunately, traditional compressors may be designed to operate primarily when loaded a certain amount (e.g., fully loaded and operating at full capacity). For example, a flow angle of the refrigerant at various locations in the compressor may be a function of the operating capacity of the compressor, and an efficiency of the compressor (and certain components thereof) may be dependent on the flow angle of the refrigerant. Thus, traditional compressors may be less efficient when operating at a capacity that diverges from the primary operating mode (e.g., full capacity).

In accordance with present embodiments, the compressor of the HVAC&R system may include a variable geometry diffuser ring positioned between a rotatable impeller of the compressor and diffuser vanes of the compressor. For example, the compressor may receive the refrigerant at an inlet, and may convey the refrigerant to the impeller. The impeller includes blades which are angled with respect to a flow of the refrigerant. The blades of the rotatable impeller accelerate the refrigerant outwardly from a center of rotation of the impeller. The accelerated refrigerant may be directed toward the diffuser, which is designed to convert kinetic energy of the flow of refrigerant into pressure, for example, by gradually reducing a velocity of the flow of refrigerant. The diffuser may include stationary diffuser vanes which are angled, positioned, or otherwise oriented to enhance an efficiency of the conversion of kinetic energy into pressure, as described above. However, since the diffuser vanes are stationary, an incidence angle of a leading edge of each diffuser vane is also stationary. Further, as noted above, the flow angle of the refrigerant may change as the compressor's loading is changed. The incidence angle of the leading edge of the diffuser vane(s) may enable the most efficient conversion of kinetic energy to pressure at a particular operating capacity of the compressor, such as full capacity. Thus, in accordance with the present disclosure and as described below, the variable geometry diffuser ring may be utilized to adjust a flow angle of the refrigerant to correspond to the incidence angle of the diffuser vane, which improves an efficiency of the diffuser vane and the compressor.

For example, the variable geometry diffuser ring may be positioned between the impeller and the diffuser vane(s), and the variable geometry diffuser ring may be configured to adjust the flow angle of the refrigerant passing there through, such that the flow angle of the refrigerant corresponds to the incidence angle of the diffuser vanes. As noted below with reference to the drawings, a control system of the HVAC&R system may adjust a position of the variable geometry diffuser ring (e.g., via an actuator coupled between the variable geometry diffuser ring and the controller) based on the operating load/capacity of the compressor, thereby causing the variable geometry diffuser ring to adjust the flow angle of the refrigerant passing to the diffuser vanes. In doing so, efficiency of the compressor is enhanced over traditional embodiments at various operating loads/capacities.

Turning now to the drawings, FIG. 1 is a perspective view of an embodiment of an environment for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system 10 in a building 12 for a typical commercial setting. The HVAC&R system 10 may include a vapor compression system 14 that supplies a chilled liquid, which may be used to cool the building 12. The HVAC&R system 10 may also include a boiler 16 to supply warm liquid to heat the building 12 and an air distribution system which circulates air through the building 12. The air distribution system can also include an air return duct 18, an air supply duct 20, and/or an air handler 22. In some embodiments, the air handler 22 may include a heat exchanger that is connected to the boiler 16 and the vapor compression system 14 by conduits 24. The heat exchanger in the air handler 22 may receive either heated liquid from the boiler 16 or chilled liquid from the vapor compression system 14, depending on the mode of operation of the HVAC&R system 10. The HVAC&R system 10 is shown with a separate air handler on each floor of building 12, but in other embodiments, the HVAC&R system 10 may include air handlers 22 and/or other components that may be shared between or among floors.

FIGS. 2 and 3 are embodiments of the vapor compression system 14 that can be used in the HVAC&R system 10. The vapor compression system 14 may circulate a refrigerant through a circuit starting with a compressor 32. The circuit may also include a condenser 34, an expansion valve(s) or device(s) 36, and a liquid chiller or an evaporator 38. The vapor compression system 14 may further include a control panel 40 that has an analog to digital (A/D) converter 42, a microprocessor 44, a non-volatile memory 46, and/or an interface board 48.

Some examples of fluids that may be used as refrigerants in the vapor compression system 14 are hydrofluorocarbon (HFC) based refrigerants, for example, R-410A, R-407, R-134a, hydrofluoro olefin (HFO), “natural” refrigerants like ammonia (NH₃), R-717, carbon dioxide (CO₂), R-744, or hydrocarbon based refrigerants, water vapor, or any other suitable refrigerant. In some embodiments, the vapor compression system 14 may be configured to efficiently utilize refrigerants having a normal boiling point of about 19 degrees Celsius (66 degrees Fahrenheit) at one atmosphere of pressure, also referred to as low pressure refrigerants, versus a medium pressure refrigerant, such as R-134a. As used herein, “normal boiling point” may refer to a boiling point temperature measured at one atmosphere of pressure.

In some embodiments, the vapor compression system 14 may use one or more of a variable speed drive (VSDs) 52, a motor 50, the compressor 32, the condenser 34, the expansion valve or device 36, and/or the evaporator 38. The motor 50 may drive the compressor 32 and may be powered by a variable speed drive (VSD) 52. The VSD 52 receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor 50. In other embodiments, the motor 50 may be powered directly from an AC or direct current (DC) power source. The motor 50 may include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor.

The compressor 32 compresses a refrigerant vapor and delivers the vapor to the condenser 34 through a discharge passage. In some embodiments, the compressor 32 may be a centrifugal or mixed-flow compressor. The refrigerant vapor delivered by the compressor 32 to the condenser 34 may transfer heat to a cooling fluid (e.g., water or air) in the condenser 34. The refrigerant vapor may condense to a refrigerant liquid in the condenser 34 as a result of thermal heat transfer with the cooling fluid. The liquid refrigerant from the condenser 34 may flow through the expansion device 36 to the evaporator 38. In the illustrated embodiment of FIG. 3, the condenser 34 is water cooled and includes a tube bundle 54 connected to a cooling tower 56, which supplies the cooling fluid to the condenser.

The liquid refrigerant delivered to the evaporator 38 may absorb heat from another cooling fluid, which may or may not be the same cooling fluid used in the condenser 34. The liquid refrigerant in the evaporator 38 may undergo a phase change from the liquid refrigerant to a refrigerant vapor. As shown in the illustrated embodiment of FIG. 3, the evaporator 38 may include a tube bundle 58 having a supply line 60S and a return line 60R connected to a cooling load 62. The cooling fluid of the evaporator 38 (e.g., water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable fluid) enters the evaporator 38 via return line 60R and exits the evaporator 38 via supply line 60S. The evaporator 38 may reduce the temperature of the cooling fluid in the tube bundle 58 via thermal heat transfer with the refrigerant. The tube bundle 58 in the evaporator 38 can include a plurality of tubes and/or a plurality of tube bundles. In any case, the vapor refrigerant exits the evaporator 38 and returns to the compressor 32 by a suction line to complete the cycle.

FIG. 4 is a schematic of the vapor compression system 14 with an intermediate circuit 64 incorporated between condenser 34 and the expansion device 36. The intermediate circuit 64 may have an inlet line 68 that is directly fluidly connected to the condenser 34. In other embodiments, the inlet line 68 may be indirectly fluidly coupled to the condenser 34. As shown in the illustrated embodiment of FIG. 4, the inlet line 68 includes a first expansion device 66 positioned upstream of an intermediate vessel 70. In some embodiments, the intermediate vessel 70 may be a flash tank (e.g., a flash intercooler). In other embodiments, the intermediate vessel 70 may be configured as a heat exchanger or a “surface economizer.” In the illustrated embodiment of FIG. 4, the intermediate vessel 70 is used as a flash tank, and the first expansion device 66 is configured to lower the pressure of (e.g., expand) the liquid refrigerant received from the condenser 34. During the expansion process, a portion of the liquid may vaporize, and thus, the intermediate vessel 70 may be used to separate the vapor from the liquid received from the first expansion device 66. Additionally, the intermediate vessel 70 may provide for further expansion of the liquid refrigerant because of a pressure drop experienced by the liquid refrigerant when entering the intermediate vessel 70 (e.g., due to a rapid increase in volume experienced when entering the intermediate vessel 70). The vapor in the intermediate vessel 70 may be drawn by the compressor 32 through a suction line 74 of the compressor 32. In other embodiments, the vapor in the intermediate vessel may be drawn to an intermediate stage of the compressor 32 (e.g., not the suction stage). The liquid that collects in the intermediate vessel 70 may be at a lower enthalpy than the liquid refrigerant exiting the condenser 34 because of the expansion in the expansion device 66 and/or the intermediate vessel 70. The liquid from intermediate vessel 70 may then flow in line 72 through a second expansion device 36 to the evaporator 38.

As noted above, in accordance with present embodiments, the compressor 32 illustrated in FIGS. 2-4 (which may be included in the system of FIG. 1) may include a variable geometry diffuser ring configured to enhance an efficiency of the compressor 32. For example, the variable geometry diffuser ring is positioned to adjust a flow angle of a refrigerant therethrough. In particular, the variable geometry diffuser ring adjusts the flow angle of the refrigerant such that the flow angle corresponds to (e.g., aligns with, matches with, corresponds with, is suited for) an incidence angle of a leading edge of one or more diffuser vanes which receive the refrigerant downstream of the variable geometry diffuser ring.

For example, a position of the variable geometry diffuser ring may be instructed or controlled by a control system which determines the desired position of the variable geometry diffuser ring based on an operating capacity of the compressor 32. By way of non-limiting example, the control system may instruct the variable geometry diffuser ring, in some embodiments via an intervening actuator, to move to a retracted position of the variable geometry diffuser ring when the compressor 32 operates at fully capacity, such that a flow path of the refrigerant to the diffuser vanes is unblocked by the variable geometry diffuser ring. The control system may instruct movement of the variable geometry diffuser ring to another position of the variable geometry diffuser ring which partially blocks the flow path when the compressor 32 operates at, for example, 75% capacity. The control system may instruct/control movement of the variable geometry diffuser ring to still another position of the variable geometry diffuser ring which further blocks the flow path when the compressor 32 operates at, for example, 50% capacity. Thus, as the operating capacity or loading of the compressor 32 decreases, an amount of blockage of the flow path, which is determined by the position of the variable geometry diffuser ring, increases. In doing so, the flow angle of the refrigerant is corresponded to (e.g., aligned with) the incidence angle of the leading edge of the one or more diffuser vanes. These and other features will be described in detail with reference to later figures below.

FIG. 5 is a cross-section of an embodiment of a portion of the compressor 32 which may be included in any of FIGS. 1-4. A refrigerant flow 99 is illustrated through the compressor 32, whereby the refrigerant flow 99 extends through blades 102 of an impeller 100 of the compressor 32, toward a diffuser passage 103 having one or more diffuser vanes 104 disposed therein, and into a collector 106. It should be noted that the illustrated refrigerant flow 99 indicates a general direction of flow, but should not be taken to indicate exact flow angles at any particular location of the compressor 32.

The blades 102 of the rotating impeller 100 accelerate the refrigerant outwardly from a center of rotation of the impeller 100. The accelerated refrigerant may travel along the illustrated refrigerant path 99 toward the diffuser passage 103, which is designed to convert kinetic energy of the refrigerant flow 99 into pressure, for example, by gradually reducing a velocity of the refrigerant flow 99. The diffuser vanes 104 may be stationary, and may be angled, positioned, or otherwise oriented to enhance conversion of the kinetic energy of the refrigerant flow 99 into pressure, as described above. In general, the diffuser vanes 104 may each include a leading edge 105 which is angled to improve efficiency of the compressor 32 at a particular operating capacity, such as full capacity, when the diffuser passage 103 is unblocked by a variable geometry diffuser ring 108 described in detail below. The collector 106 of the compressor 32 receives the pressurized refrigerant, for distribution to a downstream chiller component.

As noted above, the compressor 32 may include a variable geometry diffuser ring 108 disposed in, or proximate to, a lower portion of the diffuser passage 103 (e.g., between the impeller 100 and the diffuser vanes 104). The variable geometry diffuser ring 108 includes an adaptable position configured to enhance efficiency of the diffuser vanes 104 and, more generally, the compressor 32. For example, the variable geometry diffuser ring 108 may be coupled to an actuator 112 which, upon instruction by a controller 114, actuates or moves the variable geometry diffuser ring 108 from a previous position to a desired position. The controller 114 may control the position of the variable geometry diffuser ring 108 such that the variable geometry diffuser ring 108 adjusts a flow angle of the refrigerant flow 99 to correspond to an operating capacity of the compressor 32, as described in detail below.

The controller 114 may include a processor 116 and a memory 118, where the memory 118 includes instructions stored thereon that, when executed by the processor 116, cause the controller 114 to perform certain acts. For example, the controller 114 may control an operating capacity of the compressor 32 based at least in part on certain operating and/or environmental conditions (e.g., refrigerant temperature). The controller 114 may also include data stored to the memory 118 indicating a desired position of the variable geometry diffuser ring 108 based on the operating capacity of the compressor 32. Thus, when the controller 114 controls the operating capacity of the compressor 32, the controller 114 may also control a position of the variable geometry diffuser ring 108 which will cause the flow angle of the refrigerant flow 99 to correspond to the incidence angle of the leading edge 105 of the diffuser vane(s) 104. In one example, at full operating capacity, the controller 114 may instruct the variable geometry diffuser ring 108 to move to a fully retracted position of the variable geometry diffuser ring 108 (e.g., retracted into a cavity of a sidewall 109 adjacent the diffuser passage 103 of the compressor 32), such that the variable geometry diffuser ring 108 does not block the refrigerant flow 99. At 50% operating capacity, the controller 114 may control movement of the variable geometry diffuser ring 108 to a position which protrudes the variable geometry diffuser ring 108 into the refrigerant flow 99 (e.g., in the diffuser passage 103). For example, FIG. 6 is a cross-section of a portion of the compressor 32 of FIG. 5 having the variable geometry diffuser ring 108 in a partially blocking position. As shown in FIGS. 5 and 6, the variable geometry diffuser ring 108 is generally configured to travel along direction 110 and, as shown in FIG. 6, may restrict a portion of the diffuser passage 103 to a width 114 that is less than a total width 115 of an unblocked portion of the diffuser passage 103.

In FIGS. 5 and 6, the variable geometry diffuser ring 108 includes a rectangular cross-section. In FIG. 6, a protruding surface 116 of the variable geometry diffuser ring 108 forms a short-side of the rectangular shape, and a sliding surface 118 of the variable geometry diffuser ring 108 forms a long-side of the rectangular shape. However, in another embodiment, the sliding surface 118 may form the short-side of the rectangular shape, and the protruding surface 116 may form the long-side of the rectangular shape.

The variable geometry diffuser ring 108 may include shapes other than the rectangle shown in FIGS. 5 and 6. For example, FIGS. 7, 8, and 9 are cross-sections of embodiments of portions of the variable geometry diffuser ring 108 for use in the compressor 32 of FIG. 5. FIG. 7 includes a square or rectangular cross-section, similar to FIGS. 5 and 6. In FIG. 8, the variable geometry diffuser ring 108 includes a pointed protruding surface 116. In other words, the variable geometry diffuser ring 108 either is a triangle or includes a triangular portion. In FIG. 9, the variable geometry diffuser ring 108 includes a curved protruding surface 116. The curvature may form a half-circle, half-oval, half-ellipse, or some other curved surface. The shape of the protruding surface 116 of the variable geometry diffuser ring 108 may be selected based on geometric or operating features of the particular compressor 32 in which the variable geometry diffuser ring 108 is disposed.

The variable geometry diffuser ring 108 may additionally or alternatively include an L-shape. For example, FIG. 10 is cross-section of an embodiment of the variable geometry diffuser ring 108 positioned in a portion of the compressor 32 of FIG. 5. In the illustrated embodiment, the protruding surface 116 and the sliding surface 119 of the variable geometry diffuser ring 108 form a portion of a leg 120 of the variable geometry diffuser ring 108, which extends from a base 122 of the variable geometry diffuser ring 108. The leg 120 and the base 122 form the L-shape, as shown. The base 122 of the L-shape may be disposed in a cavity 124 suitable for receiving the base 122, and for accommodating movement of the base 122 within the cavity 124 (e.g., as the leg 120 is protruded into, and out of, the diffuser passage 103).

FIG. 11 is a block diagram illustrating an embodiment of a method 200 of operating a compressor having diffuser vanes and a variable geometry diffuser ring. In the illustrated embodiment, the method 200 includes detecting (block 201) a refrigerant temperature. For example, the aforementioned controller may be communicatively coupled with a temperature sensor, which provides to the controller data indicative of a refrigerant temperature. As previously described, in some embodiments, the refrigerant may be water.

The method 200 also includes determining (block 202) an operating capacity or load of the compressor. For example, based on the refrigerant temperature noted above and/or other features, the controller may determine an appropriate operating capacity of the compressor. The controller may then determine and control a loading or unloading of the compressor to meet the appropriate operating capacity.

The method 200 also includes controlling (block 204) a position of a variable geometry diffuser ring based on the operating capacity of the compressor. For example, as noted above, an actuator (e.g., a motor-driven actuator) may be coupled to the variable geometry diffuser ring and may be communicatively coupled to the controller. The controller may instruct or control the actuator to move the variable geometry diffuser ring from one position to another based on a change in the operating capacity of the compressor. The actuator may then move (block 206) the variable geometry diffuser ring to the appropriate position, such that the variable geometry diffuser ring adjusts the flow angle of the refrigerant to correspond to an incidence angle of a leading edge of a diffuser vane, as described below.

In general, when operating at fully capacity, the controller may instruct the actuator to move the variable geometry diffuser ring into a fully retracted position, such as a position within a cavity of a sidewall of the compressor, whereby the variable geometry diffuser ring does not adjust a flow angle of the refrigerant received from the impeller of the compressor. When operating at less than fully capacity, the controller may instruct the variable geometry diffuser ring to move to a protruded, whereby the variable geometry diffuser ring is positioned in the flow path of the refrigerant (e.g., between the impeller and the diffuser vane) such that it adjusts the flow angle of the refrigerant to correspond to an incidence angle of the diffuser vane. In other words, when operating at less than full capacity, the flow angle of the refrigerant may differ from the incidence angle of the leading edge of the diffuser vane in a way that, absent the variable geometry diffuser ring, reduces the efficiency of the diffuser vane in converting the kinetic energy of the refrigerant to pressure. By selectively positioning the variable geometry diffuser ring based on the % capacity of the compressor, the flow angle of the refrigerant is corrected to correspond to the incidence angle of the leading edge of the diffuser vane.

As set forth above, the present disclosure may provide one or more technical effects useful in improving an efficiency of a compressor of an HVAC&R system, and more particularly, to improving an efficiency of a diffuser vane of the compressor by utilizing a variable geometry diffuser ring. The variable geometry diffuser ring is positioned, based on instruction of a controller, to adjust a flow angle of the refrigerant to correspond to the incidence angle of the leading edge of the diffuser vane. In some embodiments, when the compressor operates at full capacity, the variable geometry diffuser ring is in a fully retracted position which does not adjust the flow angle. By selectively positioning the variable geometry diffuser ring to ensure an appropriate flow angle of the refrigerant proximate to the diffuser vane, an efficiency of the diffuser vane (and compressor) is improved across different operating capacities. The technical effects and technical problems in the specification are examples and are not limiting. It should be noted that the embodiments described in the specification may have other technical effects and can solve other technical problems.

While only certain features and embodiments have been illustrated and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the disclosure, or those unrelated to enabling the claimed disclosure). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation. 

1. A compressor, comprising: an impeller; a diffuser passage comprising a diffuser vane therein; a variable geometry diffuser ring positioned between the impeller and the diffuser vane with respect to a flow of a refrigerant through the compressor; and an actuator configured to move the variable geometry diffuser ring in a direction transverse to the flow of the refrigerant, and between a plurality of ring positions including a fully retracted ring position in which the variable geometry diffuser ring does not block the flow of the refrigerant, and at least one protruded ring position in which the variable geometry diffuser ring adjusts an angle of the flow of the refrigerant upstream of the diffuser vane.
 2. The compressor of claim 1, comprising a controller configured to instruct the actuator to move the variable geometry diffuser ring between the plurality of positions based at least in part on an operating capacity of the compressor, a temperature of the refrigerant, or both.
 3. The compressor of claim 1, comprising a controller configured to instruct the actuator to move the variable geometry diffuser ring between the plurality of ring positions based at least in part on an incidence angle of a leading edge of the diffuser vane.
 4. The compressor of claim 3, wherein the controller is configured to instruct the actuator to move the variable geometry diffuser ring such that the angle of the flow of the refrigerant proximate to the diffuser vane corresponds to the incidence angle of the leading edge of the diffuser vane.
 5. The compressor of claim 1, wherein the actuator is a motor-driven actuator.
 6. The compressor of claim 1, wherein the diffuser vane is stationary.
 7. The compressor of claim 1, wherein the variable geometry diffuser ring comprises a rectangular cross-sectional shape.
 8. The compressor of claim 1, wherein the variable geometry diffuser ring comprises at least a portion having a triangular cross-sectional shape, a curvilinear cross-sectional shape, or an L-shaped cross-sectional shape.
 9. The compressor of claim 1, comprising a collector positioned downstream from the diffuser passage and configured to receive the refrigerant after the refrigerant is pressurized by the diffuser vane.
 10. The compressor of claim 1, wherein the variable geometry diffuser ring is positioned within the diffuser passage.
 11. A heating, ventilation, air conditioning, and refrigeration (HVAC&R) system, comprising: a compressor comprising a diffuser vane, and having a variable geometry diffuser ring positioned upstream of the diffuser vane with respect to a flow of a refrigerant therethrough; and a controller configured to control a position of the variable geometry diffuser ring based at least in part on an operating capacity of the compressor and at least in part on an incidence angle of a leading edge of the diffuser vane.
 12. The system of claim 11, wherein the diffuser vane is stationary.
 13. The system of claim 11, comprising an actuator coupled to the variable geometry diffuser ring, wherein the controller is configured to control the position of the variable geometry diffuser ring by instructing the actuator to move the variable geometry diffuser ring to the position.
 14. The system of claim 13, wherein the actuator is a motor-driven actuator.
 15. The system of claim 11, wherein the controller is configured to control the variable geometry diffuser ring to move the variable geometry diffuser ring to at least one protruding position that corresponds to the compressor operating at less than full capacity, wherein the variable geometry diffuser ring is disposed in the diffuser passage in the at least one protruding position, wherein the controller is configured to control the variable geometry diffuser ring to move the variable geometry diffuser ring to a fully retracted position of the variable geometry diffuser ring that corresponds to the compressor operating at full capacity, and wherein the variable geometry diffuser ring is not disposed in the diffuser passage in the fully retracted position.
 16. The system of claim 11, wherein the variable geometry diffuser ring comprises a rectangular cross-sectional shape.
 17. The system of claim 11, comprising a collector positioned downstream from the diffuser passage and configured to receive the refrigerant after the refrigerant is pressurized by the diffuser vane.
 18. A method of operating a compressor, comprising: detecting a temperature of a refrigerant; determining, via a controller, an operating capacity of the compressor based at least in part on the temperature of the refrigerant; and controlling a position of a variable geometry diffuser ring based at least in part on the operating capacity of the compressor and at least in part on an incidence angle of a leading edge of a diffuser vane of the compressor.
 19. The method of claim 18, comprising actuating, via an actuator, the variable geometry diffuser ring from a previous position to the position based on a change in the operating capacity of the compressor.
 20. The method of claim 18, comprising determining that the operating capacity of the compressor is fully capacity, and instructing the position of the variable geometry diffuser ring such that the variable geometry diffuser ring is fully retracted from a flow path of the refrigerant. 